This invention relates generally to logging-while-drilling systems and more particularly to an improved uphole system for receiving data being telemetered to the surface of the earth by means of a continuous acoustic signal passing upward through the drilling fluid.
In one such logging-while-drilling system, the sensing apparatus located within the borehole transmits the logging measurements by means of an insulated electrical conductor extending upward to the surface of the earth through the drill string. In another such logging-while-drilling system, the logging measurements are transmitted uphole by means of an acoustic wave passing upward through the drill string. An example of such a system is disclosed in U.S. Pat. No. 2,810,546 to B. G. Eaton et al. In yet another such system, drilling mud within the borehole is utilized as the transmission medium for the information-bearing acoustic waves. An example of such a system is disclosed in U.S. Pat. No. 3,309,656 to John K. Godbey. In the Godbey system, drilling mud is continuously circulated downward through the drill string and drill bit and upward through the annulus provided by the drill string and the borehole wall, primarily for the purpose of removing cuttings from the borehole. An acoustic transmitter located downhole continuously interrupts the flow of the drilling mud, thereby generating an acoustic signal in the drilling mud. The acoustic wave is modulated with information measured downhole by sensing apparatus, and the modulated acoustic signal is telemetered uphole to the surface of the earth through the drilling mud. At the surface, the modulated acoustic signal is detected and demodulated to provide the desired readout information.
U.S. Pat. No. 3,789,355 of Bobbie J. Patton, issued Jan. 29, 1974, and entitled METHOD OF AND APPARATUS FOR LOGGING WHILE DRILLING, describes a logging-while-drilling system wherein telemetry of information to the surface of the well is accomplished by phase modulation of an acoustic signal. An acoustic signal is generated and transmitted upward through the drilling mud to a remote uphole station. The acoustic signal is modulated between two phase states in response to digitally coded data bits produced as a function of a downhole condition. A change in phase represents a bit of one character and a lack of change in phase represents a bit of a different character. An uphole receiving system produces an output signal representative of the phase state of the received acoustic signal. This is converted to bit clock pulses which define the bit time intervals and a bit value signal representing the generated bits.